Cu(II)-Catalyzed Annulative Sulfonylimination of α-Carbonyl-γ-alkynyl Sulfoxonium Ylides through Sulfoxonium Ylide Elimination for Access to ()-1-Isochromenes.

1-Isochromene scaffolds are ubiquitous in natural products and significant bioactive molecules. Although several methods for these molecular syntheses have been developed, reports on the efficient construction of iminated isochromenes are still rather limited. Herein, we report a new Cu(II)-catalyzed annulation and sulfonylimination cascade of α-carbonyl-γ-alkynyl sulfoxonium ylides with sulfamides, enabling direct C-C σ-bond elimination to furnish iminated ()-1-isochromenes in 51-97% yields. During the reaction process, the sulfoxonium ylide unit as a traceless eliminative group is the key to successful sulfonylimination, which enables Cu(II)-catalyzed N-H insertion and subsequent acetic acid-mediated C-C σ-bond elimination.